There is a case where the dental treatment must proceed to the next step after the confirmation of the sedation and treatment effect of a morbid part. In this case, a dental material is used to protect the infected part which has been sedated and temporarily compensate for a lost part. This dental material must be removed after a certain period of time. Therefore, the dental material needs to have such properties as ease of removal. In a prosthetic treatment, the production of a prosthetic appliance such as an inlay or crown which is produced outside the oral cavity takes at least a few days. Therefore, a dental composition (to be referred to as “temporary prosthetic appliance” hereinafter) as a substitute for a drilled tooth must adhere to tooth and must be held in a cavity formed by removing dental caries or a lost part for a certain period of time. Further, ease of removal is also required as the temporary prosthetic appliance must be removed after the completion of the prosthetic appliance. Since tooth and the temporary prosthetic appliance have been held simply by mechanical retention force, there are many problems to be solved, such as the occurrence of separation between them by a temperature change in the oral cavity or by occlusal force when food is chewed in, the breeding of bacteria due to the formation of a space, or the onset of pain.
Before the dental treatment of a dental pulp disease or an apical periodontal disease is carried out, a root canal treatment for cutting off the infection route between the root canal and the periodontal tissue or between the root canal and the oral cavity is widely carried out by filling a pulp cavity or a root canal formed when a nerve (dental pulp) is removed with a stable substance to close the space. To carry out the root canal treatment again when the initially treated part is infected unfortunately, a temporary sealing material is used to temporarily cut off the root canal infected part in the jawbone from the outside world until it is sedated. Even for the root canal treatment after sedation, there is known a method in which a root canal is filled with root filler gutta-percha filling material which is a rubber-like composition comprising natural resin gutta-percha and zinc oxide as the main ingredients together with a cement and a sealer to be mechanically stuffed and sealed. It is desired that this root filling material and the sealer should be removable for the recurrence of an infected part.
Details of the required conditions for the ideal root canal filling material are suggested by Grossman as described in Grossman, L. I.: Endodontic practice; 10th ed., Lea & Febiger, Philadelphia, 296-302, 1981. That is, the ideal root canal filling material has (1) high flowability that it is easily manipulated and ample working time (time during which it can be handled), (2) high dimensional stability, (3) ability to seal a root canal in both lateral and vertical directions, (4) no irritation to periapical tissues, (5) imperviousness to water, (6) insolubility without being corroded, (7) ability to prevent the growth of bacteria, (8) X-ray contrast properties, (9) no change in the color of tooth, (10) abacterial properties and (11) removability.
Most of existing materials are epoxy-based resins, resin-based curable compositions and glass ionomer cements which comprise polyacrylic acid and aluminosilicate glass as the main ingredients and are said to be cured through an acid-base reaction, besides the above-described root filling gutta-percha. Most of them are thermoplastic resins which are provided with X-ray contrast properties by blending an X-ray impermeable filler. These resins are heated to be provided with flowability right before they are applied to be filled into a root canal and cured while they achieve the same temperature as the temperature of the body. Since these resins have no interaction with the root canal wall, they are unsatisfactory in terms of the sealability of the root canal wall and adhesion to the root canal wall. Further, as they do not have adhesion to a sealer and a gutta-percha point, the root canal cannot be bonded and sealed completely clinically.
Lack of sealability and adhesion causes the inclusion of extraneous foreign matter into the dentine of the root canal, and the disintegration of a dental root and a bad influence upon the alveolar bone are conceivable due to the poor hygiene of the inside of the root canal. Further, since adhesion to the root canal wall by means of a thermoplastic resin of the prior art can be almost unexpected, there is possibility that sealability and adhesion may be impaired when mechanical or physical external force is applied to the root canal wall. Meanwhile, there is proposed an adhesion material for bonding enamel or dentine which is rich in calcium component as compared with the inside of the root canal.
Up till now, the following proposals have been made as root canal filing materials.
JP-A 49-5143 proposes a filling material for the treatment of a dental caries which comprises tributyl borane as a polymerization initiator. However, since it is not used as a root canal filling material, its cured product has no X-ray contrast properties and does not comprise a polymerizable monomer containing an acid group which should be interacted with the root canal wall.
Although JP-A 52-113089 discloses an aluminum oxide filler as a dental material, it is not used as a root canal filling material and therefore high X-ray contrast properties cannot be provided to this filler.
JP-A 59-15468 has a description of various fillers which do not show satisfactory X-ray contrast properties. X-ray contrast properties can be provided to the filler described in the above proposal when it is used in a composition but a root canal cannot be filled with it as its flowability degrades. The adhesive material of the proposal comprises a component which can interact with the surface of tooth. However, as it is not used to fill a root canal, its operation time is extremely short or it has no X-ray contrast properties or no sufficiently high sealability.
WO98/16187 proposes a root canal filling composition which comprises a thixotropy providing agent for adjusting viscosity and flowability and an X-ray impermeable filler as well as a pre-treatment material suitable for use in the composition. Although the proposed material has excellent manipulation ease and performance as a root canal filling material, when the thixotropy providing agent and the X-ray impermeable filler are kept in a mixed state, there is a case where target manipulation ease is not obtained due to separation or settling caused by the difference in specific gravity between them.
JP-A 2005-314326 proposes a root canal filling curable composition which comprises two different types of X-ray impermeable fillers which are fine particles having a particle diameter of 0.001 to 1 μm and particles having a particle diameter of 2 to 50 μm, can adjust viscosity and flowability by their weight ratio without containing a thixotropy providing agent for adjusting viscosity and flowability and has excellent dentine adhesion and root canal sealability. However, there is a case where it is difficult to remove the cured root canal filling curable composition when retreatment of root canal is needed.
A root canal filling composition comprising two different types of zirconium oxides which differ in particle diameter is suggested in the magazine of the Japanese Society of Conservative Dentistry, vol. 46, No. 5, pp. 690-706, 2003 as a composition described in WO98/16187. However, when the composition is kept for a long time, there is a case where target manipulation ease is not obtained due to separation or settling.